Photocurable compositions are well known in the art for forming printing plates and other photosensitive articles. In the field of photosensitive flexographic printing plates, the uncured plate typically includes a support and a photocurable surface or layer. Additional layers or surfaces on the plate can include, for example, slip films and/or release layers to protect the photocurable surface. Prior to processing the plate, the release layer typically is removed, and the photocurable layer is exposed to radiation in an imagewise fashion. Unexposed areas of the photocurable layer are then removed in developer baths.
In the past, unexposed ares of the photocurable layer were removed using developer baths comprising organic solvents. However, the toxicity, volatility, and low flash point of such solvents gave rise to hazardous conditions and polution problems. As a result, there has been a recognition in the art of the need to provide photocurable compositions which can be developed in, for example, aqueous solvents.
A flexographic printing plate not only should possess a photocurable layer which can be developed in aqueous solvents, but also should have sufficient flexibility to wrap around a printing cylinder and sufficient structural integrity to withstand the rigors experienced during typical printing processes. The printing plate also should be soft enough to facilitate ink transfer during printing, and should exhibit solvent resistant to inks, including resistance to the various organic and aqueous-based inks which are used in flexographic printing.
Many of the aqueous developable compositions reported to date have not possessed a sufficient balance of these desired properties. Consequently, there still remains a need in the art for photocurable polymers which can be dispersed in aqueous solvents and exhibit an appropriate balance of the other properties required for the production of flexographic printing plates.